DESCRIPTION The parent project for this FIRCA application studies three aims: 1) To characterize the interaction between FKBP12 and the skeletal muscle ryanodine receptor (RyR1); 2) To identify the FKBP associated with cardiac muscle ryanodine receptor (RyR2) and analyze its functional role; and 3) To determine whether the proline isomerase activity of FKBP12 plays a role in modulating cardiac and skeletal muscle ryanodine receptor function. This proposed collaboration will: 1) Characterize the role of FKBP12 in facilitating coupled gating between two or more skeletal muscle ryanodine receptors (RyR1); 2) Examine the role of FKBP12 in the activation of RyR1 by the voltage-dependent calcium channel (VDCC)/dihydropyridine receptor during E-C coupling in skeleta muscle; and 3) Determine whether FKBP effects activation of the cardiac RyR2 during E-C coupling in cardiac muscle. The FIRCA proposal makes use of new perspectives based on recent experiments identifying sequences in the II-III loop of the skeletal VDCC as activators of RyR1 during E-C coupling. The general aim is to exploit the remarkable powers of combining the biophysical investigations of individual openings of Ca channels produced in exogenous expression systems (like sf 9 cells). The investigators will use single channel measurements in artificial bilayers. The working hypothesis is that receptor/channel cooperation is central in modulating channel responses. They suggest that FKBP is a novel endogenous regulator of skeletal muscle RyR1 With FKBP12 associated to it, two RyR1/Ca release channels gate cooperatively resulting in twice the normal full conductance openings. To better understand how FKBP is involved in regulating RyR1/Ca release channel function, they propose: 1) to use drugs (FK506) and rapamycin) that inhibit the effects of FKBP12 on channel gating; and 2) determine whether mutations in the FKBP12 binding site on RyR1 affect coupled gating.